The repair of hard metal assemblies of boiling or pressurized water-cooled nuclear power facilities must comply with the requirements of 10 CFR 50.55a which includes by reference the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code.
Nuclear reactors and other components of nuclear power facilities are made of hard metal, i.e., steel and other relatively hard alloys and therefore present fastening problems that soft materials such as wood,plastics or aluminum do not. The technicians servicing nuclear power facilities are normally operating in the "field" away from their normal machine shops and other work facilities and typically must accomplish the necessary repairs in the irradiated environment of a nuclear reactor or associated steam system. An example of such repairs would be a reactor shield support repair.
The problem of making hard metal component assemblies using fasteners which "meet code" can be better understood with reference to the above mentioned ASME code and supporting requirements such as "RDT Standard M6-2T (S-935), Mechanical Locking Devices." Clearly, fasteners used in plastics, soft metals and wood are not appropriate as hard metal fasteners. Moreover, to machine fastener insert cavities or counterbores in nuclear sub-assemblies or components in the field can be a problem, particularly if irradiated parts of a nuclear reactor are involved. This is especially true because the standards for nuclear applications under the above mentioned standards for "Mechanical Locking Devices" states "A Class A locking device is designed to capture and retain fragments in the event of failure of either the locking device or fastener". A bolt locking device for repair of hard metal assemblies of boiling or pressurized water-cooled nuclear power facilities must meet the Class A requirement because fragments otherwise can become circulating debris in the reactor coolant which can do serious damage, such as by penetration of fuel rod cladding.